Effects of Whey Protein Supplementation on Muscle Damage, Hepatic Stress, and Inflammatory Markers in Power‐ and Endurance‐Trained Athletes

This study investigated the effects of 8 weeks of whey protein supplementation (30 g/day) on biomarkers of liver function, inflammation, and muscle damage in trained power-trained (predominantly speed-power/anaerobic-power disciplines) and endurance-trained athletes, in a randomized, double-blind, placebo-controlled design. Fifty-nine male athletes were stratified into power (n = 30) and endurance (n = 29) groups, then randomly assigned to a whey protein group (WG) or a placebo control group (CG). Biomarkers assessed pre- and post-intervention included alanine aminotransferase (ALT), aspartate aminotransferase (AST), C-reactive protein (CRP), and creatine kinase (CK). Significant reductions in ALT, AST, and CK were observed in both endurance- and power-trained athletes after supplementation (p = 0.001, p = 0.015, p = 0.001, and p = 0.003 respectively), indicating attenuated hepatic and muscular stress. Among the four biomarkers, only ALT displayed a statistically significant three-way interaction (Time × Supplementation × Training modality; p = 0.003), identifying it as the sole marker showing a genuine modality-specific differential response to supplementation. A significant within-group reduction in CRP was additionally observed in the supplemented power-trained athletes (p = 0.039), whereas endurance athletes showed only minor, non-significant changes; because the omnibus three-way interaction for CRP was not significant, this finding is reported as a within-group trend rather than evidence of a differential effect between modalities. Placebo groups demonstrated stable or increased enzyme and CRP values, particularly in endurance athletes. These findings suggest that whey protein may attenuate exercise-induced hepatic and muscular stress across training modalities, with a modality-specific effect on hepatic stress markers (ALT) observed in power-trained athletes. The results highlight whey protein's potential as a nutritional aid to promote recovery and physiological adaptation, possibly mediated by antioxidant and anti-inflammatory mechanisms. Further studies are warranted to examine long-term outcomes and dose-response effects across different training profiles.